Update Package.swift to correctly encode revision kind as "revision"

[ollieatkinson]

Short description 📝

@natanrolnik noticed that we had a bug when specifying a requirement to a revision:

We received an error that we couldn't handle:
    - Localized description: The data couldn't be read because it is missing.
    - Error: keyNotFound(CodingKeys(stringValue: "kind", intValue: nil), Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "packages", intValue: nil), _JSONKey(stringValue: "Index 0", intValue: 0), CodingKeys(stringValue: "requirement", intValue: nil)], debugDescription: "No value associated with key CodingKeys(stringValue: \"kind\", intValue: nil) (\"kind\").", underlyingError: nil))"

Solution 📦

Correctly encode "revision" to kind

[pepicrft]

Ouch, good catch. Thanks for fixing it @ollieatkinson. I pushed a commit to update the CHANGELOG.